African Journals Online
South African Journal of Animal Science

Volume 32, Issue 3, 2002
ABSTRACTS

Genetic and environmental parameters for ewe productivity in Merinos

Duguma, G.; Schoeman, S.J.; Cloete, S.W.P.; Jordaan, G.F.

Abstract: Data of 3272 lambing records collected on 818 ewes born from 689 dams and sired by 371 rams were used in the evaluation of ewe lifetime productivity (total number born, number weaned and total weight weaned). These records were collected from ewes born from 1969 to 1994 and which gave birth during the period from 1971 to 1999. Year of birth of ewe and ewe two-tooth liveweight affected the ewe productive traits investigated. Multiple born ewes were superior both in total number of lambs born and weaned compared to singles. Heritability estimates of 0.23, 0.17 and 0.20 were obtained for total number of lambs born (TLB), total number of lambs weaned (TLW) and total weight of lamb weaned per ewe over four lambing opportunities (TWW), respectively. For total weight weaned per ewe over the first lambing opportunity (TWW1) a heritability of 0.02 was estimated. Genetic correlation estimates of -0.10, 0.57 and 1.00 were obtained between TWW1 and TLB, TWW1 and TLW and TWW1 and TWW, respectively. High and positive genetic correlations ranging from 0.61 to 0.92 were estimated between ewe lifetime traits. Genetic progress could be expected when selection is applied on these traits.

Application of a sex identification technique in juvenile ostriches and its potential application in Botswana

Mine, O.M.; Mochakana, M.E.; Mpapho, T.; Motlhanka, D.T.M.; Kgwatalala, P.

Abstract: Sexing ostrich chicks and juveniles before the dimorphous appearance of the plumage that starts at 14 months of age is proving difficult and cumbersome for Botswana farmers. This problem delays early selection of birds for breeding and trading. It also means that birds are often sold as a mixture of males and females. DNA-based sex identification provides a solution and is amenable to large-scale application. The application of the multiplex polymerase chain reaction (PCR) was used to determine the sex of 6-months old juvenile ostriches. The blood from four mature males and four mature females were used to verify the assay. The test group consisted of 19 randomly selected six-month old birds, which turned out to be 10 males and nine females. The PCR technique uses two pairs of primers. The primers SS1 and SS2 amplify a 650 base pair (bp) female-specific fragment, while the primers L014a and L014b amplify a fragment about 280 bp, from both sexes. The females were thus distinguished by amplification of two bands after agarose gel electrophoresis, and the males by one band. Following the successful application of this technique using DNA extracted from blood, further investigations have to be conducted, using DNA extracted from other body tissue samples such as feathers or skin. A scenario is envisaged whereby, during tagging of the chicks, a body tissue sample such as a blood feather could be sent to the laboratory for DNA sexing. This technique would aid farmers in identifying the sex of their birds at a young age.

The influence of outliers on a model for the estimation of crossbreeding parameters for weaning weight in a beef cattle herd

Aziz, M.A.; Schoeman, S.J.; Jordaan, G.F.

Abstract: Data on 17348 weaning weight records from a beef cattle crossbreeding operation were used to determine the effect of outliers on regression coefficients. Different criteria were used for detecting potential influential points. Eliminating a small number (932 or 5.4%) influential points resulted in the improvement of the model fitted. The R2 values increased from 41% to 49% while the mean square error was reduced from 672.9 to 500.4. The use of diagnostic statistics for detecting influential observations is recommended before any analysis is performed.

The effect of heterogeneity for yearling weights measured in different test phases of the South African National Beef Cattle Improvement Scheme

Van der Westhuizen, R.R.; Rust, T.

Abstract: In animal breeding, animals originating from different environments are often considered in selection decisions. Production data in these groups may differ both in mean and variance. In South Africa, yearling weights of beef cattle are recorded in two different phases of the National Beef Cattle Improvement Scheme (NBCIS). The aim of this study was to assess changes in the ranking of animals in the selection process where animals are selected on estimated breeding values (EBVs) for yearling weight before and after correcting for heterogeneity between the two phases. Yearling weights are measured in Phases B and D of the NBCIS. Yearling weights recorded in Phase D were adjusted according to the standard deviation and heritabilities of yearling weights in Phase B. To determine whether the adjustment was justified, two VCE REML analyses were performed on combined Phase B and D data to estimate breeding values. The first analysis involved unadjusted Phase D data, while the second run involved Phase D yearling weights, adjusted for heterogeneity. The ranking correlation between EBVs derived from the two runs, was 99% indicating almost no re-ranked after adjustment. It is concluded that Afrikaner yearling weights in Phase B and D can be analysed jointly without any pre-adjustments when estimating breeding values.

Effects of various dietary n-3 / n-6 fatty acid ratios on the performance and body composition of broilers

Coetzee, G.J.M.; Hoffman, L.C.

Abstract: Different combinations of saturated and unsaturated fatty acids were fed to broilers to establish their effect on the fatty acid composition of the broiler carcass and the abdominal fat pad. Six combinations of Canola acid oil (CAO, high levels of C18:3n-3 and monounsaturated fatty acids) and Famarol acid oil (FAO, high levels of C18:2n-6 and saturated fatty acids) were included in the broiler diets from one day of age to six weeks of age, viz. 100% FAO, 80% FAO-20% CAO, 60% FAO-40% CAO, 40% FAO-60% CAO, 20% FAO-80% CAO, 100% CAO. There were no statistically significant differences between dietary groups in weight gain (1.71 ± 0.059 kg) or feed conversion ratios (1.97 ± 0.051 g feed/g gain). No significant differences between treatments were found in the moisture (66.20 ± 0.112%), protein (17.63 ± 0.484%), lipid (15.92 ± 1.507%) and ash (0.95 ± 0.115%) concentration of the carcasses, nor in the moisture (28.77 ± 0.112%), protein (3.03 ± 0.484%), lipid (63.32 ± 9.789%) and ash (0.45 ± 0.135%) concentrations of the abdominal fat pads. With the increase in dietary CAO levels, the mean percentages of C18:2n-6 and C20:4n-6 in the carcasses decreased respectively with 1.78% units from 20.88% and 0.35% units from 1.05%, whilst C18:3n-3 and longer chain n-3 fatty acids such as C20:5n-3 and C22:6n-3 increased respectively with 2.25% units from 1%, 0.1% units from 0.1% and 0.67% units from 0.2%. The same tendency was seen in the abdominal fat pads where C18:2n-6 and C20:4n-6 decreased respectively with 1.55% units from 20.75% and 0.98% units from 1.2% with an increase in dietary CAO, whilst C18:3n-3, C20:5n-3 and C22:6n-3 increased respectively with 2.13% units from 1.15%, 0.45% units from 0.03% and 0.95% units from 0.05%. The n-3 / n-6 ratio in the carcasses and abdominal fat pads increased respectively with 0.16% units from 0.06% and 0.19% units from 0.06% with an increase in dietary CAO. These results clearly indicate that dietary CAO enriched with á-linolenic acid lowered the saturated fatty acid concentrations in broiler carcasses and abdominal fat pads with 4.88% units and 10.63% units respectively, and increased the monounsaturated fatty acid concentrations with 3.87% units and 7.25% units, respectively and polyunsaturated fatty acid concentrations with 1.02% units and 2.38% units, respectively. The results of this experiment showed that substitution of Famarol oil with Canola oil in broiler diets can increase the ratio of n-6 to n-3 fatty acids in broiler carcasses and abdominal fat pads to 5:1, a ratio more suitable for human health. Increasing the level of n-3 fatty acids in the diets was also effective in reducing the level of saturated fatty acids in the carcasses and abdominal fat pads of broiler chickens resulting in "healthier" chickens.

Impacts of intervention objectives in goat production within subsistence farming systems in South Africa

Braker, M.J.E.; Udo, H.M.J.; Webb, E.C.

Abstract: The aims of this research were to study goat production in the rural areas of South Africa and to explore the impact of intervention objectives, namely an increase in kidding percentage and a decrease in kid losses (mortalities, theft and predation) on goat production in subsistence farming systems. A personal interview survey was conducted in three communities in South Africa, namely Jericho (Northwest Province), Bolahlakgomo (Northern Province) and Schoonoord (Northern Province). In each community, traditional purposes and meat consumption were important reasons for keeping goats. Other reasons mentioned were used to characterise the systems and were commercially-orientated in Jericho, social reasons in Bolahlakgomo and of a supportive nature in Schoonoord. The average herd size was 16.2 animals in Jericho, 7.7 animals in Bolahlakgomo and 40.1 animals in Schoonoord. The most important expenses incurred were for veterinary products, while that for feed and veterinary services were relatively low. Most important outputs included the slaughter for home consumption, sale of live animals and ceremonial uses. Mortalities were similar in the three communities; theft was high in Jericho and predation was high in Bolahlakgomo. Economic values based on gross margin calculations were R864 in Jericho, R382 in Bolahlakgomo and R1, 569 in Schoonoord. Intervention objectives yielded economic values of R1, 887 in Jericho and R934 in Bolahlakgomo. No intervention objectives were proposed for Schoonoord. From this research it is concluded that intervention objectives have different outcomes in different communities. The success of commercialisation of livestock production in general is based on the location of the community, accessibility of knowledge and markets, and production goals of the household.

Declawing ostrich (Struthio camelus domesticus) chicks to minimize skin damage during rearing

Meyer, A.; Cloete, S.W.P.; Brown, C.R.; Van Schalkwyk, S.J.

Abstract: Leather is one of the main products derived from ostrich farming. Current rearing practices lead to a high incidence of skin damage, which decreases the value of ostrich skins. In the emu and poultry industry, declawing is commonly practiced to reduce skin damage and injuries. We consequently investigated declawing of ostrich chicks as a potential management practice to minimize skin lesions that result from claw injuries. A group of 140 day-old ostriches was declawed and a second group of 138 chicks served as the control. The two groups were reared separately to slaughter, but were rotated monthly between adjacent feedlot paddocks to minimize possible paddock effects. Overall, the declawed group had fewer scratch and kick marks on the final processed skin than the control group, which resulted in the proportion of first grade skins in the declawed group being more than twice that of the control group. Behavioural observations at nine and 13 months of age indicated that declawing resulted in no impairment in locomotive ability or welfare. There was a tendency for the declawed group to have higher average live weights towards the end of the growing-out phase that resulted in a 3.7% higher average skin area at slaughter than in the control group. Survival to slaughter was independent of the treatment group, but absolute means favoured the control group. It was concluded that declawing does not compromise the wellbeing of ostriches and has a significant benefit in terms of the quality and the grading of the skin, with important economic implications for ostrich farmers.